As mobile terminals increase, a user equipment (UE) has increasing data volume requirements. Currently, bandwidth of a frequency band lower than 6 GHz is no longer sufficient to meet increasing requirements on communication performance. Therefore, using a high frequency band having rich bandwidth resources as a frequency for backhaul and access will become a trend. The high frequency band is a frequency band higher than 6 GHz, for example, 30 GHz to 300 GHz, or higher.
However, compared with a frequency band lower than 6 GHz, one of obvious characteristics of a high frequency band is high path loss. To ensure a propagation distance, a high frequency beam needs to be relatively narrow. However, coverage of a narrow beam system is limited. Therefore, to obtain an antenna gain as much as possible, narrow beam scanning and alignment need to be performed between a network device and a terminal device, thereby implementing normal communication between the network device and the terminal device.
To implement narrow beam scanning and alignment, beam training needs to be performed. In a beam training phase, a BS (base station) allocates a different training sequence to each UE. However, training sequences are limited. Assuming there are 10 sequences, a maximum of 10 UEs can be simultaneously beam-trained. If there are 50 UEs needing to be trained, the 50 UEs need to be separately trained in five different time periods. Because one of main high-frequency scenarios is a user-intensive scenario, overheads of beam training are relatively high.